Tetramethoxymethylglycoluril crosslinking agents are known. They are prepared by etherification of tetramethylolglycoluril with excess methanol under acidic conditions. The unreacted methanol is then removed under basic conditions to prevent acid catalyzed oligomerization of tetramethoxymethylglycoluril.
Tetramethoxymethylglycoluril chemistry is described in the following references: U.S. Pat. Nos. 4,118,437; 4,064,191; 4,877,838; 4,105,708; 4,520,167; 3,927,024 and 4,137,213; British Patent Number 1,562,971 and 2,010,875; German Patent Number 920,146 (Chemical Abstracts, Volume 52 (1958), page 11, 469 d, e, and f) and Houben-Weyl Makromolekulare Stoffe, Volume XIV, Part 2, page 353. In the prior art processes for the preparation of tetramethoxymethylglycoluril above, the unreacted methanol is removed by distillation under basic conditions.
Several aspects of tetramethoxymethylglycoluril chemistry are described in an article entitled "Chemistry of glycoluril-formaldehyde resins and their performance in coatings," Journal of Coatings Technology, Volume 51, Number 658, pages 101 to 110, 1979. Further aspects of glycoluril chemistry are described in the following articles entitled "Advances in the chemistry of N-containing crosslinking agent," Textile Research Journal, Volume 41, pages 239 to 254, 1971, and "New Crosslinking Agents for Durable Powder Coatings," Proceedings of the 16th International Conference in Organic Coating Science and Technology, Athens, Greece, Volume 16, pages 509 to 524, Jul. 9 to 13, 1990.
U.S. Pat. Nos. 4,101,520 and 4,293,692 describe methylolated and etherified melamines
Powder coatings prepared from teramethoxymethylglycoluril are described in U.S. Pat. Nos. 4,118,437; 4,254,235; 4,255,558; 4,683,271; 4,877,838; and 4,346,144.
Acid catalyzed oligomerization of etherified glycolurils during the removal of alcohols after neutralization with caustic soda or under acidic conditions is described in the British Patent Number 848,400.
The preparative methods of the prior art comprise methylolating glycoluril with formaldehyde, etherifying the resulting tetramethylolglyco uril with excess methanol under acidic conditions, and isolating the reaction product, typically by separating the unreacted methanol by distillation under basic conditions. The distillation is carried out under basic conditions to prevent any potential acid catalyzed oligomerization of tetramethoxymethylglycoluril. However, under the basic conditions of the prior art, an undesirable demethylolation side reaction takes place and, as a result of the demethylolation, products having few methoxymethyl groups are obtained.
Obtaining methoxymethylated glycolurils of high functionality such as those having four methoxymethyl groups per each glycoluril moiety is highly desirable because systems having fewer than four methoxymethyl groups exhibit a diminished efficiency to act as crosslinking agents. In cases where the tetramethoxymethylglycoluril prepared by the methods of the prior art is highly functionalized with methoxymethyl groups, it also contains high levels of oligomers. In cases where the tetramethoxymethylglycoluril contains low levels of oligomers, it also is of low methoxymethyl functionalization. Thus, the tetramethoxymethylglycolurils prepared by the methods of the prior art have either low levels of oligomers accompanied by substantially less than four methoxymethyl groups per glycoluril moiety, or high levels of oligomers accompanied by low levels of the highly functionalized tetramethoxymethylglycoluril. It is therefore desirable to be able to prepare highly functionalized and highly monomeric tetramethoxymethylglycoluril.
It is the object of this invention to provide a process for preparing a substantially fully methylolated, substantially fully etherified, substantially monomeric tetramethoxymethylglycoluril.